Dielectric-loaded field applicator for EHID lamps and EHID lamp assembly containing same

Abstract

A dielectric-loaded field applicator and an EHID lamp assembly are provided wherein the applicator comprises a helical resonator having a cylindrical dielectric core and a helical conductor, the dielectric core having a helical groove extending along its surface substantially from end to end; the helical conductor being contained in the helical groove and connectable at one end to a power source, the dielectric core being comprised of a dielectric material having a relative permittivity greater than about 3, preferably polycrystalline alumina. The EHID lamp assembly includes two opposed dielectric-loaded applicators with a discharge vessel supported between them.

I claim: 
     
       1. A dielectric-loaded field applicator for an EHID lamp, comprising:
 a helical resonator having a cylindrical dielectric core and a helical conductor, the dielectric core having a helical groove extending along its surface substantially from end to end; 
 the helical conductor being contained in the helical groove and connectable at one end to a power source, the dielectric core having a recess for holding a discharge vessel and being comprised of a dielectric material having a relative permittivity greater than about 3. 
 
     
     
       2. The applicator of  claim 1 , wherein the dielectric material has a relative permittivity greater than about 5. 
     
     
       3. The applicator of  claim 1 , wherein the dielectric material has a relative permittivity of at least about 10. 
     
     
       4. The applicator of  claim 1 , wherein the dielectric material is fused silica. 
     
     
       5. The applicator of  claim 1 , wherein the dielectric material is polycrystalline alumina. 
     
     
       6. The applicator of  claim 1 , wherein the applicator has an EMI shield surrounding the helical resonator. 
     
     
       7. The applicator of  claim 6 , wherein the EMI shield is cylindrical in shape and substantially concentric with the helical resonator. 
     
     
       8. The applicator of  claim 1 , wherein the helical conductor has a circumferential length defined by 
       
         
           
             
               
                 π 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 d 
               
               ≤ 
               
                 
                   
                     λ 
                     o 
                   
                   
                     2 
                     ⁢ 
                     
                       ɛ 
                     
                   
                 
                 . 
               
             
           
         
       
     
     
       9. An EHID lamp assembly, comprising:
 two opposed dielectric-loaded field applicators and a discharge vessel disposed between the applicators; 
 the discharge vessel containing a discharge medium and being supported at opposite ends by the applicators; 
 the applicators each comprising a helical resonator having a cylindrical dielectric core and a helical conductor, the dielectric core having a helical groove extending along its surface substantially from end to end, the helical conductor being contained in the helical groove and connectable at one end to a power source, the dielectric core being comprised of a dielectric material having a relative permittivity greater than about 3; and 
 the discharge vessel and the two applicators being arranged along, and coaxial with, a common axis. 
 
     
     
       10. The assembly of  claim 9 , wherein the dielectric core of each applicator has a recess for supporting the discharge vessel. 
     
     
       11. The assembly of  claim 9  wherein the discharge vessel is supported between the applicators by a refractory cement. 
     
     
       12. The assembly of  claim 9 , wherein the dielectric core is comprised of polycrystalline alumina. 
     
     
       13. The assembly of  claim 9  wherein the helical conductor is a metal wire. 
     
     
       14. The assembly of  claim 9  wherein the helical conductor has a circumferential length defined by 
       
         
           
             
               
                 π 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 d 
               
               ≤ 
               
                 
                   
                     λ 
                     o 
                   
                   
                     2 
                     ⁢ 
                     
                       ɛ 
                     
                   
                 
                 . 
               
             
           
         
       
     
     
       15. The assembly of  claim 9  wherein each applicator has an EMI shield that is cylindrical in shape and is substantially concentric with the helical resonator. 
     
     
       16. The assembly of  claim 15  wherein the EMI shield is comprised of a quartz tube having a conductive coating of indium tin oxide. 
     
     
       17. An EHID lamp assembly, comprising:
 two opposed dielectric-loaded field applicators and a discharge vessel disposed between the applicators; 
 the discharge vessel containing a discharge medium and being supported at opposite ends by the applicators; 
 the applicators each comprising a helical resonator having a cylindrical dielectric core and a helical conductor, the dielectric core having a helical groove extending along its surface substantially from end to end, the helical conductor being contained in the helical groove and connectable at one end to a power source, the dielectric core being comprised of polycrystalline alumina and having a recess for supporting the discharge vessel; 
 the discharge vessel and the two applicators being arranged along, and coaxial with, a common axis, and each applicator having an EMI shield that is cylindrical in shape and substantially concentric with the helical resonator. 
 
     
     
       18. The assembly of  claim 17  wherein the discharge vessel is in contact with the dielectric core of each applicator. 
     
     
       19. The assembly of  claim 17  wherein the EMI shield is comprised of a quartz tube having a conductive coating of indium tin oxide. 
     
     
       20. The assembly of  claim 17  wherein the EMI shield is comprised of a metal wire mesh.